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[PATCH 2/5] cfq-iosched: Reorder checks in cfq_should_preempt()

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From: Jan Kara <jack@suse.com>

Move check for preemption by rt class up. There is no functional change
but it makes arguing about conditions simpler since we can be sure both
cfq queues are from the same ioprio class.

Signed-off-by: Jan Kara <jack@suse.com>
---
 block/cfq-iosched.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fcef1786edf3..b78a82acf99c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3959,6 +3959,13 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
 	if (cfq_slice_used(cfqq))
 		return true;
 
+	/*
+	 * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
+	 */
+	if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
+		return true;
+
+	WARN_ON_ONCE(cfqq->ioprio_class != new_cfqq->ioprio_class);
 	/* Allow preemption only if we are idling on sync-noidle tree */
 	if (cfqd->serving_wl_type == SYNC_NOIDLE_WORKLOAD &&
 	    cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
@@ -3973,12 +3980,6 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
 	if ((rq->cmd_flags & REQ_PRIO) && !cfqq->prio_pending)
 		return true;
 
-	/*
-	 * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
-	 */
-	if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
-		return true;
-
 	/* An idle queue should not be idle now for some reason */
 	if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
 		return true;
-- 
2.6.2

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[PATCH 2/5] cfq-iosched: Reorder checks in cfq_should_preempt() Jan Kara <jack@suse.cz> - 2016-01-07 16:30 +0100
  Re: [PATCH 2/5] cfq-iosched: Reorder checks in cfq_should_preempt() Tejun Heo <tj@kernel.org> - 2016-01-08 18:00 +0100

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